<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>Document</title>
  </head>
  <body>
    <script>
      var year = prompt('请输入年份');
      if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
        alert('您输入的年份是闰年');
      } else {
        alert('您输入的年份是平年');
      }
    </script>
  </body>
</html>